1. Field of the Invention
The present invention relates to an electron beam-writing apparatus capable of writing a plurality of desired patterns on a semiconductor substrate in one shot, as well as to an electron beam-writing method using the apparatus.
2. Description of the Prior Art
With the ever improving fineness of semiconductor devices in recent years, the lithography technology used in production of semiconductor devices is changing from light exposure to electron beam writing (electron beam exposure). Electron beam writing can provide high resolution but has a problem of low throughput. To solve the low-throughput problem, there were developed a method described in Japanese Patent Application Laid-Open (Kokai) No. 54-29981 and methods called one-shot exposure method, block-by-block exposure method or part-by-part exposure method. In one of these conventional methods, an electron beam emitted from an electron gun is shaped into a square beam by a first aperture means; the square beam is applied onto a second aperture means (a transfer mask) having desired patterns formed therein; an electron beam of desired patterns which has passed through the second aperture means, is applied onto a semiconductor wafer for writing (transferring). A representative apparatus used in this method is schematically explained with reference to FIG. 1. An electron beam 3 emitted from an electron beam source 2 is shaped by a first beam-shaping aperture means 4 and a second beam-shaping aperture means 8 and is applied onto a sample 9 placed on a sample stage 10. The electron beam 3 emitted from the electron beam source 2 has a Gaussian distribution (that is, has a nearly circular section) and, as shown in FIG. 10, the aperture 102 of the first beam-shaping aperture means 100 has a square shape in order to effectively utilize an electron beam-applied area 101.
When, by using a first beam-shaping aperture means 100 shown in FIG. 10, cell patterns 40 of memory device are formed on a sample (a semiconductor wafer) 9, as shown in FIG. 4, by part-by-part exposure method and in that case, there is used a maximum writing area 110 (see FIG. 11) formed on the first beam-shaping aperture means 100, for achieving high throughput, the patterns 112 on a second beam-shaping aperture means consist of, for example, 7 patterns in X direction and 3 patterns in Y direction as shown in FIG. 11. By repeatedly writing this unit block on the wafer, cell patterns 40 of memory device as shown in FIG. 4 are formed. The number of cell patterns of memory device is ordinarily 2.sup.n. However, when the cell patterns 40 are formed by repeated writing of a unit block consisting of 7 patterns in X direction and 3 patterns in Y direction, the number of cell patterns formed is not 2.sup.n and there appears pattern shortage or pattern excess at the last row and column. To remedy this problem, therefore, it is necessary that part-by-part writing is conducted up to the row and column right before the last row and column and that variable shaping writing is conducted for the last row and column. In this approach, there are required, in addition to the pattern shot data for part-by-part writing, data preparation for variable shaping writing, data planning, and position matching between part-by-part writing and variable shaping writing, etc., resulting in increased operational steps and increased time. To reduce steps required for data preparation for variable shaping writing, data planning, and position matching between part-by-part writing and variable shaping writing, etc., it is necessary that the number of patterns in the unit block used in conducting writing is a number satisfying 2.sup.n as in an example of a block 111 (shown in FIG. 11) consisting of 4 patterns in X direction and 2 patterns in Y direction.
As stated above, when writing is conducted using a maximum square writing area 110 as shown in FIG. 11, 21 patterns [7 patterns (in X direction).times.3 patterns (in Y direction)] can be written and satisfactory writing throughput is obtained. However, in view of the steps required for data preparation, position matching, etc., the actual writing throughput is low.
When each pattern of device has a shape long in X direction and short in Y direction as shown in FIG. 12 (120 is a maximum writing area), the unit block 121 of patterns 122, formed on a second beam-shaping aperture means must have a rectangular shape (long in X direction and short in Y direction) in order for the number of patterns in the unit block to be 2.sup.n (2.sup.2 =4 in FIG. 12). If the unit block has a square shape, the writing area is inevitably insufficient in X direction and inevitably excessive in Y direction. Similarly, when each pattern of device has a shape short in X direction and long in Y direction as shown in FIG. 13 (130 is a maximum writing area), the unit block 131 of patterns 132, formed on a second beam-shaping aperture means must have a rectangular shape (short in X direction and long in Y direction) in order for the number of patterns in the unit block to be 2.sup.n (2.sup.2 =4 in FIG. 13). If the unit block has a square shape, the writing area is inevitably insufficient in Y direction and inevitably excessive in X direction. While reduction in steps required for data preparation, position matching, etc. is desired, the reduction is achieved by using the square block 121 or 131 and increasing the number of shots. In the case of FIG. 14 described in Japanese Patent Application Laid-Open (Kokai) No. 3-64016, one pair of patterns is long in X direction and, therefore, the number of patterns in X direction is small when a square maximum writing area is used. As a result, the unit writing block is inevitably rectangular (X&gt;Y). In this type of writing, however, two shots are required in order to form one pair of patterns, resulting in even lower throughput.
In a conventional electron beam-writing apparatus as shown in FIG. 1, the first beam-shaping aperture means has, as shown in FIG. 10, a square aperture in order to effectively utilize an electron beam-applied area 101 (having a circular shape owing to the Gaussian distribution of the electron beam applied). When the pattern formation of memory device is conducted by part-by-part writing method (or one-shot writing method), the number of patterns in unit block is 2.sup.n in order to reduce the steps required for pattern data preparation, position matching between part-by-part writing area and variable shaping writing area, etc. When one shot is allowed to include a plurality of unit blocks each having 2.sup.n patterns (examples of the unit block are shown in FIGS. 11, 12, 13 and 14), the writing area is slightly insufficient in Y direction in FIG. 11 or FIG. 13 and in X direction in FIG. 12 or FIG. 14. Therefore, allowing one shot to include a plurality of small unit blocks has been difficult. This has allowed one shot to include only one unit block, making it impossible to achieve high writing throughput. Further, in patterns as shown in FIG. 14, since there are supplementary patterns in X direction, the number of patterns in Y direction is small as compared with the number of patterns in X direction, making it impossible to achieve high throughput.